<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div {
            width: 300px;
            height: 40px;
            border: 1px solid black;
            text-align: center;
            line-height: 40px;
        }
    </style>
</head>

<body>

    <div></div>
    <script>
        const div = document.querySelector('div')
        const time_set=1000
        function Mydate() {
            let date = new Date()
            let h = date.getHours();
            let m = date.getMinutes();
            let s = date.getSeconds();
            h = h < 10 ? '0' + h : h
            m = m < 10 ? '0' + m : m
            s = s < 10 ? '0' + s : s
            return `今天是:${date.getFullYear()}年${date.getMonth()+1}月${date.getDate()}日
            ${h}时${m}分${s}秒`
        }
        div.innerHTML = Mydate()
        setInterval(function(){
            div.innerHTML = Mydate()
        },time_set)
    </script>
</body>

</html>